Abstract
Abstract. Oil palm is the most rapidly expanding tropical perennial crop. Its cultivation raises environmental concerns, notably related to the use of nitrogen (N) fertilisers and the associated pollution and greenhouse gas emissions. While numerous and diverse models exist to estimate N losses from agriculture, very few are currently available for tropical perennial crops. Moreover, there is a lack of critical analysis of their performance in the specific context of tropical perennial cropping systems. We assessed the capacity of 11 models and 29 sub-models to estimate N losses in a typical oil palm plantation over a 25-year growth cycle, through leaching and runoff, and emissions of NH3, N2, N2O, and NOx. Estimates of total N losses were very variable, ranging from 21 to 139 kg N ha−1 yr−1. On average, 31 % of the losses occurred during the first 3 years of the cycle. Nitrate leaching accounted for about 80 % of the losses. A comprehensive Morris sensitivity analysis showed the most influential variables to be soil clay content, rooting depth, and oil palm N uptake. We also compared model estimates with published field measurements. Many challenges remain in modelling processes related to the peculiarities of perennial tropical crop systems such as oil palm more accurately.
Highlights
Oil palm is the most rapidly expanding tropical perennial crop
Beside issues related to land use changes and the oxidation of peat soils when establishing plantations, the cultivation of oil palm can generate adverse environmental impacts, in particular through the use of nitrogen (N) fertilisers
We may assume that other models exist, which we could not access or calibrate, but those tested very likely provide a representative sample of modelling possibilities for simulating the N budget of oil palm plantations
Summary
The area of land under oil palm, currently amounting to approximately 19 Mha, has been rising at 660 000 ha yr−1 over the 2005–2014 period (FAOSTAT, 2014), and this trend is likely to continue until 2050 (Corley, 2009) Beside issues related to land use changes and the oxidation of peat soils when establishing plantations, the cultivation of oil palm can generate adverse environmental impacts, in particular through the use of nitrogen (N) fertilisers. The latter are associated with pollution risks for ground and surface waters, and emissions of greenhouse gases (Choo et al, 2011; Comte et al, 2012; Corley and Tinker, 2003). Models appear necessary in this process because comprehensive direct measurements of N losses are too difficult and resourceintensive to be generalised
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